Compare lactulose vs. Metamucil

Head-to-head comparisons of medication uses, side effects, ratings, and more.



Relieves constipation and gets rid of ammonia in people with liver problems. Generlac (lactulose) relieves constipation and high ammonia levels, but it can take up to 48 hours to work.Helps get things moving. The natural psyllium fiber in Metamucil (Psyllium) does more than relieve constipation. It lowers cholesterol, keeps blood sugar levels healthy, and makes you feel less hungry between meals.
Find lowest prices
Powered by GoodRxSave on your next prescription. Be sure you’re getting the lowest price for your medication, even if you have insurance.
Reviews & ratings
Filter group. All currently selected
Filter group. All currently selected

Not enough reviews for this treatment. Help someone out, leave a review!

Have you used Generlac (lactulose)?
Worth itNot sureNot worth it
Reviews for Metamucil
+29% better vs. lactulose
+55% better vs. lactulose
+10% better vs. lactulose
454 reviews
Have you used Metamucil (psyllium)?
Worth itNot sureNot worth it
Side effects

The lactulose FDA package insert doesn’t have numbers about how common side effects are.

More about lactulose side effects »

We haven’t found good data for Metamucil side effects.

FDA side effect reports for Metamucil »
How it works
Generlac (lactulose) draws water into the intestines to soften your stool for easier passing. It also helps draw ammonia into your stool for removal from the body.Metamucil (Psyllium) is a fiber-based laxative. It adds bulk and moisture to your intestine, which softens stool and makes it easier to pass.
Type of medication
Prescription onlyOver-the-counter
Available as
  • Liquid
  • Powder
  • Liquid
Used for
Risk factors for serious side effects
  • Taking Generlac (lactulose) for more than 6 months
  • Elderly
  • Taking medications that cause mineral imbalance
  • Not exercising regularly
  • Diabetes
Detailed Generlac (lactulose) risks & warnings »
  • Age 60 or older
  • Malignancy
  • Other condition that causes blockage or narrowing of bowel
  • Taking medications that cause constipation
  • Sensitivity to psyllium
Detailed Metamucil (psyllium) risks & warnings »

The FDA hasn’t classified this medicine’s effects on unborn babies. Talk with your doctor about this medicine if you’re pregnant or planning on it.

No food related info.
  • Talk to you doctor about eating certain foods and getting more exercise to help prevent your constipation.
Upsides and benefits
  • Generlac (lactulose) is the first-choice treatment for brain conditions caused by high ammonia levels.
  • Can be used if you have severe chronic constipation leading to blockage.
  • Available in generic.
  • Can be taken orally or rectally.
  • Psyllium is the most recommended brand of natural fiber laxative
  • Some people feel that taking Psyllium is a hassle, but most think it's worth it.
  • It has multiple health benefits, good to control your hunger between meals, improves your blood sugar and lowers cholesterol levels.
  • Studies show it works better than a stool softener for constipation.
Downsides and risks
  • Should not be used if you are on a galactose-restricted diet.
  • Does not provide rapid relief of constipation. Talk to your doctor or pharmacist if you need quick relief.
  • Generlac (lactulose) has a very sweet flavor that most people don't like.
  • You may have to take Psyllium daily for 1-3 days to see full effects.
  • If you don't take it with enough liquid, it could swell, block your throat and cause choking.
  • Not the best choice for people who have swallowing problems or aren't able to drink lots of liquids.
  • Psyllium contains psyllium. Don't take if you have an allergy to psyllium from breathing it in or swallowing it.
  • Can cause gas and mild belly cramps.
Tips from our pharmacists for people taking the medication
  • Generlac (lactulose) works within 24 to 48 hours to produce a bowel movement.
  • If you are taking this for constipation, it is usually taken once a day.
  • The goal is for you to have 2 to 3 stools a day.
  • You can mix the oral solution in juice, water, or milk for better taste.
  • Generlac (lactulose) can cause you to be dehydrated, so make sure you drink plenty of fluids.
  • Maintaining a healthy diet, regular exercise, and drinking plenty of fluids can help you prevent constipation.
  • Psyllium works in about 12-72 hours for constipation.
  • It's important to take each dose with at least 8 ounces (a full glass) of water or other liquid (not hot liquids).
  • Mix powder well and drink right away up to 3 times a day (build up to this slowly), but not for more than one week.
  • Don't take Psyllium within 2 hours before or after taking other medicines. It may interact and affect how they work.
  • If you take Psyllium then have chest pain, vomiting, trouble breathing or swallowing, get medical help immediately.
  • Ask your doctor before taking Psyllium if you have stomach pain, nausea, vomiting or had sudden changes in your stool for more than 2 weeks.
  • Ask your doctor about giving Psyllium to anyone younger than 12 years.
  • Stop taking Psyllium and call your doctor if you have pain, swelling or bulging in your belly, rectal bleeding or have not had a bowel movement after taking.
  • Talk to you doctor about eating certain foods and getting more exercise to help prevent your constipation.
Learn more
More about lactuloseSide effectsReviews & ratingsAlternativesFDA package insert
Have you used Generlac (lactulose)?
Worth itNot sureNot worth it
More about MetamucilSide effectsReviews & ratingsAlternativesFDA package insert
Have you used Metamucil (psyllium)?
Worth itNot sureNot worth it